1. Field of the Invention
The present invention relates to a motor-driven valve used for flow control of a refrigerant in a refrigeration cycle system and others.
2. Description of the Related Art
As the above-mentioned motor-driven valve, in Patent document 1 is proposed a motor-driven valve with a driving mechanism for contacting and separating a valve body to/from a valve seat by utilizing a rotation of a rotor of an electric motor, and in the fully-closed state of the valve, an upper stopper body fixed to a valve shaft holder collides against a lower stopper body fixed to a guide bush to finish rotational downward movement of a valve shaft. This motor-driven valve adopts, in opening direction of the valve, a screw disengagement construction, in which the valve shaft holder is finally disengaged from the guide bush fixed to a valve main body to finish upward movement of the valve shaft.
Further, in Patent document 2 is proposed a motor-driven control valve comprising: a valve section having a valve seat, a valve body, etc.; and a stepping motor section situated above the valve section to contact and separate the valve body to/from the valve seat through rotation of a rotor, and the motor-driven control valve is provided with an opening limit stopper and a closing limit stopper above the rotor in a closed case.
Further, in Patent document 3, as illustrated in FIG. 15, is described a motor-driven valve 110 comprising: a valve main body 115 having a first flow passage 112 and a second flow passage 113 that communicate a valve chamber 111 and having a valve seat part 114 at a portion of the second flow passage 113 communicating with the valve chamber 111; a rod-shaped needle valve 117 contacting and separating to/from a valve seat 116 of the valve main body 115; a cylindrical closed case 119; a stator coil 127 disposed outside of the closed case 119; a rotor 124 that is movable in the closed case 119 in a direction that the valve opens/closes while rotating through magnetization by feeding current to the stator coil 127 and is provided with a cylindrical sleeve 122, and a cylindrical permanent magnet 123 fixed by a stop ring 126 outside the sleeve 122; and a male screw pipe 121 for opening and closing the needle valve 117 through a screw feed mechanism by the rotation of the rotor 124, in which a lower cover 120 for the closed case 119 is fixed through welding to the valve main body 115.
In this motor-driven valve 110, on a lower end portion of the sleeve 122 projects an upper closing limit stopper portion 122a, and on a flange body 118 projects a lower closing limit stopper portion 118a, in the closed state of the needle valve 117, the upper closing limit stopper portions 112a contacts with the lower closing limit stopper portion 118a to prevent the rotor 124 from further downwardly moving in the closed state of the valve.    [Patent document 1] Japanese Patent Publication No. 2006-70990 gazette.    [Patent document 2] Japanese Utility Model Publication No. Heisei 3-9565 gazette.    [Patent document 3] Japan Patent No. 3310042 gazette.
However, the screw disengagement construction of the motor-driven valve in the direction that the valve opens as shown in Patent document 1 cannot be adopted to a motor-driven valve with such construction as the engagement between the valve shaft holder and the guide bush cannot be released.
Further, in the motor-driven control valve described in Patent document 2, the opening/closing limit stoppers are positioned above the rotor, so that total length of the motor-driven control valve becomes long, and the number of parts used for the opening/closing limit stoppers becomes large as well, which causes deterioration of assembling workability of the valve, resulting in increased manufacturing cost. In addition, when such opening/closing limit stoppers are tried to be disposed in the rotor, it is necessary to shorten outer diameter of the valve shaft holder to provide a space for disposing the limit stoppers, in accordance with this, it becomes difficult to secure a space for mounting a coil spring for urging the valve body. As a result, there was a problem that downsizing of the motor-driven valve while maintaining a large valve port diameter is difficult.
Still further, in the motor-driven valve 110 described in Patent document 3 shown in FIG. 15, at an initialization processing, for instance, in which the motor-driven valve is driven to close the valve with the number of pulses beyond overall stroke from the fully-opened position to the fully-closed position to forcibly transit the opening of the motor-driven valve to the fully-closed state, the upper closing limit stopper portion 122a downwardly moving in accordance with the rotation of the rotor 124 contacts with the lower closing limit stopper portion 118a, which generates frequent impact sounds, so that using this motor-driven valve 110 for room air conditioners or the like results in a problem of deterioration of housing environment.
In addition, it is necessary to construct the motor-driven valve 110 such that the upper closing limit stopper portion 122a and the lower closing limit stopper portion 118a do or do not contact with each other during one rotation of the sleeve 122, so that areas of the both stopper portion 122a, 118a that contact with each other are set small, which causes a problem of shortened life of the motor-driven valve 110 as a product due to wear and deterioration of the both stopper portions 122a, 118a caused by the above-mentioned impacts.
Especially, in a motor-driven valve like the above motor-driven valve 110 with a coil spring 130 urging the needle valve 117 to the valve seat 116 after the needle valve 117 is seated on the valve seat 116 until the upper closing limit stopper portion 122a contacts with the lower closing limit stopper portion 118a, that is, the fully-opened state, the coil spring 130 relaxes the impact to a certain degree when the upper closing limit stopper portion 122a collides against the lower closing limit stopper portion 118a. On the other hand, a motor-driven valve with simple construction without such coil spring 130 has a serious problem of the above impacts.